The key with the modern double-breasted look, Estreicher told us,
is that it's shorter and slimmer than the traditional cut.

You should be able to wear it casually in Spring and Summer too,
so think lighter colors — gray, dark blue, white.

"But casual or not," said Estreicher, "the double-breasted
pitfall will always be the cut and fit. Look out for the bulk of
the extra fabric and the boxiness of the shoulders. For best look
and fit, consult with a tailor. This is a fit that can be more
complex than the regular 1 button suit and will benefit from some
expert advice and touch ups to the waist area."

So, unless you have your jacket custom-fitted, make sure someone
with a tailor's eye gives your jacket a second look. There's no
point in doing this unless it's done right.